Power supply system for a high frequency power amplifier

ABSTRACT

The present invention provides a power supply circuit, which supplies a power supply voltage to a high frequency power amplifier. The power supply circuit comprises a DC—DC converter, a voltage control transistor, and a control circuit which controls the voltage control transistor. When the power supply circuit is used in a CDMA-system cellular phone, the power supply circuit supplies a power supply voltage generated by the DC—DC converter to the high frequency power amplifier upon a low output, whereas upon a high output, the power supply circuit turns on the voltage control transistor to directly supply a battery voltage to the high frequency power amplifier. On the other hand, when the power supply circuit is used in a CGS-system cellular phone, the power supply circuit supplies a power supply voltage generated by the DC—DC converter to the high frequency power amplifier, whereas upon a high output, the voltage control transistor is controlled by the control circuit based on a signal for designating an output level to generate a power supply voltage supplied to the high frequency power amplifier.

BACKGROUND OF THE INVENTION

The present invention relates to a technology effective for applicationto a power supply circuit for a high frequency power amplifier, which isused in a wireless communication apparatus such as a cellular phone orthe like, and particularly to a power supply circuit available for acellular phone having a plurality of systems such as a GSM (GlobalSystem for Mobile Communication) system, a CDMA (Code Division MultipleAccess) system, etc.

As a power supply circuit for a high frequency power amplifier of acellular phone, there has currently been known a technology wherein avoltage converter circuit like a DC—DC converter and a power switchcomprising MOSFET or the like are utilized in combination, and whenoutput power is low, the power switch is turned off and a voltagestepped down by the DC—DC converter is used, whereas when the outputpower is high, the DC—DC converter is turned off and the power switch isturned on to supply a battery voltage to the high frequency poweramplifier as a source or power supply voltage as it is, therebyenhancing power efficiency of the whole system.

On the other hand, since the GSM system is higher in output power thanCDMA, a power supply circuit using a DC—DC converter is not provided,and an APC (Automatic Power Control) circuit is provided which effectsfeedback onto a gate bias circuit which detects a DC level of an outputand generates a gate bias voltage of an output power element so as toreach output power necessary for calling (see, for example, UnexaminedPatent Publication No. 2000-151310). Such a control system is generallycalled “closed loop system or type”.

However, the system of controlling the output power according to theclosed loop type has the problem that since there is a need to providethe APC circuit, a circuit scale increases correspondingly and apackaging density is reduced. Therefore, there is provided a system forcontrolling a source or power supply voltage of an output power FETbased on a signal for designating an output level, so that the outputlevel changes in proportion to the signal to thereby linearly operatethe output power FET, thus ensuring linearity of an output of a highfrequency power amplifier. This system is called an “open loop system ortype” and has the advantage of enabling a reduction in circuit scale ascompared with the closed loop system.

SUMMARY OF THE INVENTION

A standard DC—DC converter incapable of performing complex control isnow used in a CDMA-system cellular phone. However, if a power supplycircuit is configured using the standard DC—DC converter even though thecellular phone is considered to proceed toward more multi-functioningfrom now on, it is difficult to cope with the multi-functioning in thisway. If an attempt is made to configure a power supply circuit capableof performing the complex control by using standard electronic parts,then the number of parts increases and a packaging density is reduced,thus causing difficulty in reducing the size of the cellular phone.Although the cellular phone is moving toward considerably achieving areduction in power consumption, there has also been a strong need for afurther reduction in power consumption. The reduction in powerconsumption has heretofore been made with an eye to enhancing theefficiency of a high frequency power amplifier. However, only theenhancement of the efficiency of the high frequency power amplifiermakes unattainable a sufficient reduction in power consumption.

An object of the present invention is to provide a power supply circuitfor a high frequency power amplifier, which is capable of reducing powerconsumption and thereby increasing a call time of a cellular phone andthe life of a battery.

Another object of the present invention is to provide a power supplycircuit for a high frequency power amplifier, which is capable of beingused in a cellular phone capable of communicating according to aplurality of systems like a GSM system and a CDMA system and providing areduction in power consumption.

A further object of the present invention is to provide a power supplycircuit for a high frequency power amplifier, which is capable ofreducing the number of parts and thereby reducing its size in a casewhere the power supply circuit capable of performing complex controlwith multi-functioning of a cellular phone is configured.

The above, other objects and novel features of the present inventionwill become apparent from the description of the present specificationand the accompanying drawings.

Summaries of typical ones of the inventions disclosed in the presentapplication will be described in brief as follows:

A power supply circuit, which supplies a power supply voltage to a highfrequency power amplifier, comprises a voltage converter circuit of aswitching power type like a DC—DC converter, a voltage controltransistor like an FET, and a power control circuit which controls thevoltage control transistor. When the power supply circuit is used in aCDMA-system cellular phone, it supplies a power supply voltage generatedby the DC—DC converter to the high frequency power amplifier upon a lowoutput, whereas upon a high output, the power supply circuit turns onthe voltage control transistor to directly supply a battery voltage tothe high frequency power amplifier. On the other hand, when the powersupply circuit is used in a GSM-system cellular phone, the power supplycircuit supplies a power supply voltage generated by the DC—DC converterto the high frequency power amplifier upon a low output. Upon a highoutput, the voltage control transistor is controlled by a controlcircuit based on a signal for designating an output level to therebygenerate a power supply voltage supplied to the high frequency poweramplifier.

According to the above means, the power supply circuit for the highfrequency power amplifier can be shared between the CDMA-system cellularphone and the GSM-system cellular phone, for example. Thus, the numberof parts constituting the power supply circuit of the cellular phoneconfigured so as to be capable of performing communications of at leasttwo systems can be reduced, and hence the cellular phone can be broughtinto less size. Since the efficiency at the low output is enhanced inGSM-system communications, current consumption decreases and thecellular phone using the power supply circuit is capable of increasing acall time and the life of a battery.

Further, a power supply circuit for a high frequency power amplifier,which is used in a CDMA-system cellular phone configured so as to becapable of detecting an output level of the high frequency poweramplifier to thereby control a bias voltage of the high frequency poweramplifier, is made up of a DC—DC converter, a voltage controltransistor, and a control circuit for controlling the voltage controltransistor. In a first mode or a system (closed loop) in which theoutput level of the high frequency power amplifier is detected tocontrol the bias voltage of the high frequency power amplifier, a powersupply voltage produced by the DC—DC converter is supplied to the highfrequency power amplifier upon a low output, whereas upon a high output,the voltage control transistor is turned on to directly supply a batteryvoltage to the high frequency power amplifier. On the other hand, in asecond mode or a system (open loop) for controlling the power supplyvoltage for the high frequency power amplifier without depending on asignal for detecting the output level of the high frequency poweramplifier, the voltage control transistor is controlled based on asignal for designating or specifying the output level to therebygenerate a power supply voltage corresponding to the output leveldesignating signal, followed by supply to the high frequency poweramplifier.

According to the above means, the power supply circuit for the highfrequency power amplifier can be shared between, for example, a mode orsystem in which a GSM-system cellular phone performs transmission in aclosed-loop system or type, and a mode or system in which it performstransmission in an open loop system or type. Thus, the number of partsconstituting the power supply circuit of the cellular phone configuredso as to be capable of performing communications of at least two systemscan be reduced, and hence the cellular phone can be brought into lesssize.

Preferably, a filter circuit using a ferrite bead as an inductor isprovided at an output terminal of the DC—DC converter. Thus, noiseproduced due to a switching operation of the DC—DC converter can be cut.

Further, preferably, the power control circuit for controlling thevoltage control transistor based on the output level designating signalmakes use of a circuit which comprises an amplifier (operationalamplifier circuit) that outputs a voltage corresponding to the outputlevel designating signal, and a MOSFET having a gate controlled based onthe output of the amplifier to output a source or power supply voltageof an output power FET from its drain, and which feeds back the drainvoltage of the MOSFET to the amplifier to thereby generate a desiredpower supply voltage. When the voltage control transistor is on-offcontrolled according to the closed-loop system, the output of theamplifier is brought to full amplitude to thereby perform its on-offcontrol. Thus, the response to a control signal is improved.

Further, when the DC—DC converter makes use of a synchronous rectifyingcircuit configured so as to complementarily on-off control a firstswitch element and a second switch element connected in series between avoltage input terminal and a reference potential terminal to allow acurrent to flow through an inductor connected between a connecting nodeof the first switch element and the second switch element and an outputterminal, thereby outputting a voltage obtained by stepping down thevoltage applied to the voltage input terminal, the second switch elementis controlled so as to avoid its turning on when the output leveldesignating signal indicates a predetermined level or less, therebyoutputting a desired voltage under a switching operation of the firstswitch element. Thus, the output of the DC—DC converter varies between apower supply voltage (Vdd) and a negative potential (−0.7V) and hence anoperation margin for the DC—DC converter can be enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a schematic configuration of a powersupply circuit for a high frequency power amplifier according to thepresent invention and a system of a cellular phone using the same;

FIG. 2 is a circuit configurational diagram illustrating a specificexample of the high frequency power amplifier supplied with a powersupply voltage from the power supply circuit according to an embodiment;

FIG. 3 is a circuit configurational diagram illustrating one embodimentof the power supply circuit for the high frequency power amplifieraccording to the present invention;

FIG. 4 is a block diagram showing a schematic configuration of a systemof the CDMA cellular phone using the power supply circuit according tothe embodiment;

FIG. 5 is a block diagram illustrating a schematic configuration of asystem of the cellular phone of GSM closed-loop type, using the powersupply circuit according to the embodiment;

FIG. 6 is a block diagram depicting a schematic configuration of asystem of the cellular phone of GSM open-loop type, using the powersupply circuit according to the embodiment;

FIG. 7 is a graph showing input/output characteristics of a highfrequency power amplifier employed in the cellular phone of GSMopen-loop type, using the power supply circuit according to theembodiment;

FIG. 8 is a circuit diagram showing a configuration of an output stageof a DC—DC converter which constitutes the power supply circuitaccording to the embodiment;

FIG. 9 is a waveform diagram showing output waveforms obtained where asynchronous rectifying circuit on the ground point side of the outputstage of the DC-Dc converter of FIG. 7 is operated and cut off; and

FIG. 10 is a block diagram showing a second embodiment of a power supplycircuit for a high frequency power amplifier according to the presentinvention, and a schematic configuration of a system of a cellular phoneof a GSM open-loop type, using the power supply circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will hereinafter bedescribed in detail with reference to the accompanying drawings.Incidentally, components each having the same function in all thedrawings for describing the embodiments of the present invention arerespectively identified by the same reference numerals and theircomponents will be explained.

FIG. 1 shows one embodiment of a system where the present invention isapplied to a cellular phone transmittable and receivable by two types orsystems of a GSM system and a CDMA system. Incidentally, the GSM systemmeans a communication system in which a TDMA (Time Division MultipleAccess) system is adopted as a data multiplexed system and a GMSK(Gaussian filtered Minimum Shift Keying) system is adopted as amodulation scheme in the present embodiment. Further, the CDMA systemmeans a system of a cellular phone in which a CDMA (Code DivisionMultiple Access) system is adopted as a data multiplexed system.

In FIG. 1, ANT indicates an antenna for transmitting and receiving asignal wave, reference numeral 100 indicates a front end unit connectedto the antenna ANT, reference numeral 200 indicates a high frequencyamplifying unit including a high frequency power amplifier foramplifying a transmit signal and outputting the amplified signaltherefrom and a power supply system or circuit thereof, and referencenumeral 300 indicates a base band & modulation unit comprising a baseband circuit for converting a voice signal to a base band signal,converting a receive signal to a voice signal and generating atransmit/receive switch signal or a modulation-scheme or mode switchsignal, and a modem circuit for demodulating the receive signal togenerate a base band signal and modulating a transmit signal,respectively. The base band & modulation unit 300 comprises a pluralityof LSIs and ICs such as a DSP (Digital Signal Processor), amicroprocessor, a semiconductor memory, etc.

The front end unit 100 comprises a low-pass filter 110 connected to aGSM transmit output terminal to attenuate harmonics, a transmit/receiveselector switch circuit 120, a duplexer 130 which performsdemultiplexing of a GSM-system signal and a CDMA-system signal, anisolator 140 connected between the CDMA transmit output terminal of thehigh frequency amplifying unit 200 and the duplexer 130, etc. Thesecircuits and elements are mounted on one ceramic substrate or printedwiring board so as to be capable of being configured as a module.

A changeover signal CNT of the transmit/receive selector switch circuit120 is supplied from the base band & modulation unit 300. Receivesignals Rx (GSM) and Rx (CDMA) are supplied to the base band &modulation unit 300 via filters FLT1 and FLT2 which eliminate noise orinterference.

The high frequency amplifying unit 200 includes a high frequency poweramplifier 210 for GSM, a high frequency power amplifier 220 for CDMA, apower supply circuit 230 shared between these, a gain variable amplifier240 which amplifies a CDMA transmit signal outputted from the base band& modulation unit 300, a SAW filter 250 which allows only signals in adesired frequency band to pass therethrough, a coupler 260 which detectsan output level of the high frequency power amplifier 220 for CDMA, anautomatic power controller 270 which compares the output level detectedby the coupler 260 and a signal for designating or specifying an outputlevel supplied from the base band & modulation unit 300 and therebycontrols the gain of the gain variable amplifier 240 so that the outputlevel coincides with the designated level, etc.

The power supply circuit 230 comprises a voltage control P-channelMOSFET 231 connected between a battery 400 and a power terminal for thehigh frequency power amplifiers 210 and 220, a DC—DC converter 232 whichsteps down a voltage Vb of the battery 400, a power control circuit 233which generates a control signal used for each of the MOSFET 231 and theDC—DC converter 232, an inductor 234 connected between an outputterminal of the DC—DC converter 232 and the power terminal for the highfrequency power amplifiers 210 and 220, a smoothing condenser 235 whichstabilizes a generated source or power supply voltage, etc.

In the present embodiment, the P-channel MOSFET 231, the inductor 234and the smoothing condenser 235 are respectively made up of discreteelectronic parts. The DC—DC converter 232 and the power control circuit233 are configured as a semiconductor integrated circuit (IC). The ICand the discrete electronic parts such as the FET 231, the inductor 234,the smoothing capacitor 235, etc. are packaged on one ceramic substrateso as to be configured as a power supply module.

Incidentally, the gain variable amplifier 240 and the automatic powercontrol circuit 270 can also be formed on one semiconductor chip as asemiconductor integrated circuit. As each of the semiconductorintegrated circuit and the high frequency power amplifier 220, may beused one configured as another module (so-called RF module). When thefront end unit 100 is configured as a module, the coupler 260 can bemade up of a signal transfer microstrip line formed on a ceramicsubstrate for the front end module, and a conductor layer formed so asto be opposite to it with a dielectric layer interposed therebetween.

FIG. 2 shows a circuit configurational example of the high frequencypower amplifier 210 (220). The high frequency power amplifier 210 (220)employed in the present embodiment has a structure wherein a pluralityof field effect transistors (hereinafter called also simply“transistors”) are sequentially cascade-connected as active elements tothereby form a multistage configuration on a circuit basis. Namely, ittakes a three-stage configuration wherein a gate terminal of amiddle-stage transistor Q2 is connected to a drain terminal of afirst-stage transistor Q1, and a gate terminal of a final-stagetransistor Q3 is connected to a drain terminal of the middle-stagetransistor Q2.

In the high frequency power amplifier 210 (220) shown in FIG. 2, ahigh-frequency signal Pin is inputted to a gate terminal of thefirst-stage transistor Q1 through a capacitive element C1. A drainterminal of the final-stage transistor Q3 is connected to an outputterminal Pout through a capacitive element C4. Thus, the high frequencypower amplifier cuts a dc component of the high-frequency input signalPin and amplifies an ac component thereof, followed by its output. Anoutput level at this time is controlled based on a bias control voltageVabc and the power supply voltage Vdd from the power supply circuit 230.The bias control voltage Vabc is supplied to the gates of thetransistors Q1, Q2 and Q3 through resistors R1, R2 and R3 so that biasvoltages Vg1, Vg2 and Vg3 are applied thereto. The bias control voltageVabc is supplied from, for example, the base band & modulation unit 300according to the output level.

Incidentally, signs MS1 through MS6 in FIG. 2 respectively indicatemicrostrip lines which act as inductors for matching impedances betweenthe respective stages. Signs MS7 through MS9 respectively indicatemicrostrip lines for matching impedances between the high frequencypower amplifier and the power control circuit 233. The condensers C1,C2, C3 and C4 series-connected to the microstrip lines MS1 through MS6serve so as to cut off dc voltages of the power supply voltage Vdd andthe gate bias voltages (Vg1, Vg2 and Vg3).

In the high frequency power amplifier 210 (220), although not restrictedin particular, the final-stage transistor Q3 comprises a discrete part(output power MOSFET or the like), and the first-stage and middle-stagetransistors Q1 and Q2 and the resistors R1 and R2 are formed on onesemiconductor chip as a semiconductor integrated circuit. Further, thecondensers C1, C2, C3 and C4 are connected as external elements. Themicrostrip lines MS1 through MS9 are formed in conductive layer patternssuch as copper or the like formed so as to assume desired inductancevalues, on a ceramic substrate equipped with a semiconductor chip formedwith, for example, the transistors Q1 and Q2 and the resistors R1through R3 constituting a bias circuit 14.

A more detailed configurational example of the power supply circuit 230is illustrated in FIG. 3. The power supply circuit according to thepresent embodiment can be used even in any of the GSM closed-loopsystem, GSM open-loop system and CDMA system. Even when the power supplycircuit is used in any system, the power supply circuit is contrived ona circuit basis so that power consumption of the high frequency poweramplifier can be reduced.

In FIG. 3, Ramp indicates a control signal for designating or specifyingan output level supplied from the base band & modulation unit 300 in theGSM system. The power control circuit 233 comprises an op amplifier(operational amplifier circuit) OPA which receives Ramp as an input, afeedback circuit FDC made up of a CR circuit, which effects feedbackfrom a drain terminal of a P-channel MOSFET 231 controlled by the outputof the op amplifier OPA and set so as to take out an output voltage Vddfrom the drain terminal thereof, to a non-inversion input terminal ofthe op amplifier OPA, and a control logic CTL which generates activationsignals for the op amplifier OPA and the DC—DC converter 232, based oncontrol signals SHDN, CONT0, CONT1 and CONT2 supplied from the base band& modulation unit 300. Although not restricted in particular, the outputlevel control signal Ramp is inputted as a pulse, and the level ofamplitude of the pulse is generated so as to represent the magnitude ofa required output level.

The DC—DC converter 232 comprises a reference generator VRG whichgenerates a reference voltage Vref, like a bandgap reference circuit,switches SW1 and SW2 comprising MOSFETs, which are connected in seriesbetween a power supply or source voltage terminal Vb and a ground pointGND, a clock generation & PWM control circuit CPC which generates asignal (control pulse) applied to each of the gates of the switches SW1and SW2 to on-off control each of theses and a clock signal necessary togenerate the control pulse, a comparator CMP which compares thereference voltage Vref and a voltage obtained by feeding back an outputvoltage to thereby generate a control signal for the clock generation &PWM control circuit CPC, etc.

The power supply circuit 230 according to the present embodimentcontrols a voltage applied to the gate of the P-channel MOSFET 231 in aGSM-system open-loop mode in which the output voltage Vdd is fed back tothe non-inversion input terminal of the op amplifier OPA via the CRcircuit FDC to thereby bring the control signal SHDN supplied from thebase band & modulation unit 300 to a high level to operate the opamplifier OPA, to thereby make it possible to output a voltage Vdd whichchanges approximately linearly with respect to the input voltage Ramp.

On the other hand, the power supply circuit 230 turns off the P-channelMOSFET 231 in a CDMA-system operation mode, based on the control signalSHDN supplied from the control logic CTL when the required output levelis low, to turn on the DC—DC converter 232 so as to output the voltageproduced from the DC—DC converter 232, whereas when the required outputlevel is high, the power supply circuit 230 turns off the DC—DCconverter 232 to bring the P-channel MOSFET 231 into a completeon-state, thereby making it possible to output the voltage Vb of thebattery 400 in a through state. Incidentally, the P-channel type is usedas the output MOSFET 231 in that the output power supply voltage Vdd canbe raised up to near the battery voltage Vb as compared with anN-channel type MOSFET. It is thus possible to reduce a power loss.

Further, when the DC—DC converter 232 is operated to supply astepped-down voltage, the power supply circuit 230 according to thepresent embodiment switches the output voltage Vdd to a plurality ofstages (e.g., two stages) according to the required output level. Theswitching to the output voltage Vdd is performed as follows: Bleederresistors Rb1, Rb2 and Rb3 are provided in the course of a path forfeeding back the output voltage of the DC—DC converter 232 to thecomparator CMP to divide the output voltage by a resistance ratio. Thenthe switch SWC on the inversion input side of the comparator CMP ischanged over according to the control signal generated by the controllogic CTL based on the control signals CONT0 through CONT2 supplied fromthe base band & modulation unit 300 to thereby select and feed back anyof the voltages divided by the bleeder resistors, whereby the aboveswitching is carried out. While the bleeder resistors Rb1, Rb2 and Rb3and switch SWC for switching the output level to the two stages areshown in FIG. 3 in the interest of illustrations, the embodiment isconfigured so that the output level can be switched to three stages.

FIG. 4 shows an example of a system configuration where the CDMA systemof the cellular phone shown in FIG. 1 is operated, FIG. 5 illustrates anexample of a system configuration where the GSM system of the cellularphone shown in FIG. 1 is activated in an open-loop type or system, andFIG. 6 depicts an example of a system configuration where the powersupply circuit 230 is applied to a cellular phone of a GSM closed-loopsystem. Table 1 shows one example of the relationship betweencombinations of the control signals CONT0 through CONT2 and SHDNsupplied from the base band & modulation unit 300 to the power supplycircuit 230, their output states and operating states of the powersupply circuit in the respective systems. The CDMA system and the systemof the GSM open-loop type or system are identical to each other in therelationship between the combinations of the control signals CONT0through CONT2 and SHDN, their output states and the operating states ofthe power supply circuit. However, an output voltage Vdd in each systemcan be set so as to reach a desired level by changing a resistance ratioof bleeder resistors Rb1 through Rb3 external to the power supplycircuit.

TABLE 1 Operating state Applied system Output Control signal input DC-method state Cont0 Cont1 Cont2 SHDN PMOS DC Vout (Vdd) CDMA or GSM highoutput High High Low High On off Vb (3.6 V) closed loop through middleLow High Low High off on set output voltage of 1 to 2 V Low output LowLow Low High off on set voltage of 1.0 V or less Power Low Low Low Lowoff off — cutoff GSM open loop variable High High High High Linear off 0to Vdd output opera- tion power cutoff Low Low Low Low off off —

In the system of FIG. 4 showing the example of the system configurationwhere the power supply circuit 230 is applied to the cellular phone ofthe CDMA system, the high frequency power amplifier 210, thetransmit/receive selector switch 120, the filter 110 and the FLT1 in theGSM system are made unnecessary or respectively brought to anon-operating state.

In a power supply circuit 230, a control logic CTL brings an opamplifier OPA to a non-operating state according to a control signalSHDN supplied from a base band & modulation unit 300. When a requiredoutput level is low, the control logic CTL activates a DC—DC converter232 to supply a stepped-down voltage as a power supply voltage Vdd for ahigh frequency power amplifier 220. When the required output level ishigh, the control logic CTL turns off the DC—DC converter 232 and turnson a P-channel MOSFET 231 as an alternative to it to thereby supply abattery voltage Vb as the power supply voltage Vdd for the highfrequency power amplifier 220 as it is.

At this time, a signal for turning on the P-channel MOSFET 231 isgenerated by the control logic CTL and may be directly supplied to agate terminal of the P-channel MOSFET 231. Alternatively, the opamplifier OPA may be operated as a buffer or comparator so that theP-channel MOSFET 231 is brought to a complete on state (battery voltagethrough state) by the output of the op amplifier OPA.

Such control is performed as follows: For example, an inversion inputterminal of the op amplifier OPA inputted with an output level controlsignal Ramp in an open loop is pulled up to Vdd. When it is desired toturn off the P-channel MOSFET 231, the control logic CTL supplies Vdd toa non-inversion input terminal of the op amplifier OPA, whereas when itis desired to turn on the P-channel MOSFET 231, the control logic CTLsupplies a ground potential to the non-inversion input terminal, wherebythe above control can be carried out. Since the P-channel MOSFET 231 isan element relatively large in size and is also large in gatecapacitance, an on-off operation can be speeded up by controlling theP-channel MOSFET 231 via the op amplifier OPA rather than by directlyon/off-controlling the P-channel MOSFET 231 by the control logic CTLcomprising MOSFETs.

In a high frequency power amplifying unit, an automatic power controlcircuit 270 compares an output level detected by a coupler 260 and asignal (Ramp') for designating or specifying an output level suppliedfrom the base band & modulation unit 300 even when the required outputlevel is high and low. Further, the automatic power control circuit 270controls the gain of a gain variable amplifier 240 so that the outputlevel coincides with the designated level, and the high frequency poweramplifier 220 amplifies a high frequency transmit signal Rf-in andoutputs it therefrom.

In FIG. 5 showing the system configuration where the GSM system of thecellular phone shown in FIG. 1 is operated in the open loop system, thehigh frequency power amplifier 220 of the CDMA system, the isolator 140,the duplexer 130 and the filter FLT2 are made unnecessary orrespectively brought to a non-operating state.

In a power supply circuit 230 of this system, a control logic CTL bringsan op amplifier OPA to an operating state according to a control signalSHDN supplied from a base band & modulation unit 300. Thus, the opamplifier OPA drives a P-channel MOSFET 231 according to an output levelcontrol signal Ramp supplied from the base band & modulation unit 300 togenerate a voltage Vdd which linearly changes according to the outputlevel control signal Ramp, thereby supplying the voltage Vdd to a highfrequency power amplifier 210 as a power supply voltage Vdd and bringinga DC—DC converter 232 to a non-operating state.

Owing to the supply of the power supply voltage Vdd sent from theP-channel MOSFET 231 controlled in the above-described manner to thehigh frequency power amplifier 210, an output Vout of the high frequencypower amplifier 210 changes approximately linearly with respect to theinput voltage Ramp.

In FIG. 6 showing the example of the system configuration where thepower supply circuit 230 shown in FIG. 3 is applied to the cellularphone of the GSM closed-loop system, the high frequency power amplifier220, the isolator 140, the duplexer 130 and the filter FLT2 in the CDMAsystem are made unnecessary. As an alternative to it, there are provideda couple 260′ which detects an output level of a high frequency poweramplifier 210, and an automatic power control circuit 270′ whichcompares the output level detected by the coupler 260′ and a signal Rampfor designating an output level supplied from a base band & modulationunit 300 to thereby generate a bias voltage Vabc of the high frequencypower amplifier 210 so that the output level coincides with thedesignated level.

In the power supply circuit 230 of this closed-loop system, a controllogic CTL brings an op amplifier OPA to a non-operating state accordingto a control signal SHDN supplied from the base band & modulation unit300. When a required output level is low, the control logic CTL operatesa DC—DC converter 232 to supply a stepped-down voltage as a power supplyvoltage Vdd for the high frequency power amplifier 210. When therequired output level is high, the control logic CTL turns off the DC—DCconverter 232 and turns on the P-channel MOSFET 231 as an alternative toit to thereby supply a battery voltage Vb as the power supply voltageVdd for the high frequency power amplifier 210 as it is.

Even in this case, a signal for turning on the P-channel MOSFET 231 isgenerated by the control logic CTL and may be directly supplied to agate terminal of the P-channel MOSFET 231. Alternatively, the opamplifier OPA may be operated as a buffer or comparator so that theP-channel MOSFET 231 is brought to a complete on state (battery voltagethrough state) by the output of the op amplifier OPA.

In a high frequency power amplifying unit, the automatic power controlcircuit 270′ compares the output level detected by the coupler 260′ andthe signal Ramp for designating or specifying the output level suppliedfrom the base band & modulation unit 300 even when the required outputlevel is high and low, and thereby generates the bias voltage Vabc forthe high frequency power amplifier 210 so that the output levelcoincides with the designated level.

When the above-described power supply voltage Vdd outputted from theP-channel MOSFET 231 is supplied to the high frequency power amplifier210 up to a very low range of the required output level without the useof the DC—DC converter to activate the high frequency power amplifier210, the efficiency of the high frequency power amplifier 210 isrepresented as indicated by a curve A of FIG. 7. However, when thevoltage outputted from the DC—DC converter is supplied in the region inwhich the required output level is very low, under the application ofthe power supply circuit according to the above embodiment, theefficiency of the high frequency power amplifier 210 in the system ofthe GSM closed-loop type is represented as indicated by a curve Bdesignated at sign B of FIG. 7 where the frequency is set as 880 MHz andthe DC—DC converter 232 steps a power supply voltage Vdd of 3.5V down to1.5V, for example, and supplies it. Further, the efficiency thereof isrepresented as indicated by a curve designated at sign C of FIG. 7 wherethe DC—DC converter 232 steps the power supply voltage Vdd of 3.5V downto 1.0V and supplies it.

Owing to the application of the present embodiment in this way, theefficiency in the low output region can be enhanced. Since the cellularphone is often used at a low output rather than used at a high output,the efficiency in the low output region is improved as in the embodimentalthough the efficiency in a high output region is not so changed ascompared with the prior art. Thus, the effect of suppressing the totalpower consumption can be expected.

In the system of the present embodiment, a filter comprising a ferritebead FB and a capacitor C2 is provided between an inductor 234 and asmoothing condenser 235. This filter is capable of preventing noiseproduced by a switching operation of the DC—DC converter 232.

Further, a synchronous rectification type converter is used as the DC—DCconverter 232 in such a system as shown in FIG. 4 or 5 using the powersupply circuit 230 according to the embodiment. When the output level islow, the DC—DC converter 232 may be controlled by such a method as to bedescribed later. Thus, an operation margin can be improved.

FIG. 8 shows a configuration of an output unit of the DC—DC converter232. The DC—DC converter 232 employed in the present embodiment is oneof such a type as called a so-called synchronous rectification type,which comprises switches SW1 and SW2 each comprising a MOSFET, which isseries-connected between a power terminal Vcc inputted with a dc voltagesupplied from a battery or the like and a reference potential terminalGND like a ground point, an inductor Lx connected between the other endthereof and an output terminal OUT of the DC—DC converter, and asmoothing capacitor Cx connected to the other end of the inductor Lx.

The switches SW1 and SW2 are alternately turned on by clocks CLK1 andCLK2. When the switch SW2 is turned off and the switch SW1 is turned on,a current flows from the power terminal Vdd to the inductor Lx. When theswitch SW1 is turned off and the switch SW2 is turned on, a currentflows from the ground point to the inductor Lx. Thus, voltagescorresponding to the frequencies of the clock CLK1 and CLK2 and theirpulse widths are outputted. The clocks CLK1 and CLK2 for on-offcontrolling the switches SW1 and SW2 are respectively formed so as tohave dead times for preventing the flow of a through current due to asimultaneous on state of the switches SW1 and SW2.

In the present embodiment, a NOR gate G1 for cutting off or blocking thesupply of the clock CLK2 is provided on a supply path of the clock CLK2used to control the switch SW2 on the ground point side. A clock controlsignal CE supplied from the control logic CTL or the like is inputted tothe other input terminal of the NOR gate G1. When the required outputlevel of the high frequency power amplifier is reduced, the clockcontrol signal CE is changed to a high level. In doing so, the output ofthe NOR gate G1 is fixed to a low level so that the switch SW2 iscontinuously brought to an off state. Therefore, when the switch SW1 ischanged from on to off, the current that will continue to flow throughthe inductor Lx, is supplied through a PN junction diode Ds2 lyingbetween a source region of the switch MOSFET SW2 held in the off stateand a substrate.

As a result, a potential Vo at the output terminal OUT is set to anegative potential reduced by a forward voltage (about 0.7V) from aground potential (0V). Thus, upon the normal switching operation, theoutput of the DC—DC converter amplitude-operated between a power supplyvoltage Vdd and a ground potential GND as shown in FIG. 9(A) variesbetween the power supply voltage Vdd and—0.7V as shown in FIG. 9(B) bycutting-off of the control clock CLK2 for the switch SW2 on the groundpoint side. Therefore, an operation margin for the DC—DC converter isenhanced, and hence the DC—DC converter is capable of operation up tosuch a range that the required output level of the high frequency poweramplifier is low. Lowering the minimum output level makes it possible toreduce power consumption of the high frequency power amplifier.

On the other hand, when the power supply voltage Vdd from the aboveP-channel MOSFET 231 is supplied to the high frequency power amplifier210 to activate the high frequency power amplifier 210 up to a range inwhich the required output level is very low, in the system of the GSMopen loop type shown in FIG. 5, the output Vout of the high frequencypower amplifier 210 changes approximately linearly with respect to theinput voltage Ramp, but the efficiency of the high frequency poweramplifier 210 is decreased.

Therefore, an embodiment of a power supply circuit capable of increasingthe efficiency in a low range of a required output level even if it isused in the system of the GSM open loop type, and a configurationalexample of the system of the GSM open loop type using the same will nextbe explained using FIG. 10.

The power supply circuit according to the embodiment shown in FIG. 10 isone wherein a DC—DC converter 232 of a power supply circuit 230 isoperated in the low range of the required output level even in the caseof the system of the GSM open loop type. In the case of the use of thepower supply circuit according to the embodiment, one example of therelationship between combinations of control signals CONT0 through CONT2and SHDN supplied from a base band & modulation unit 300 to the powersupply circuit 230, their output states and operating states of thepower supply circuit in the respective systems is shown in Table 2.

TABLE 2 Applied Operating state system Output Control signal inputmethod state Cont0 Cont1 Cont2 SHDN PMOS-A PMOS-B DC-DC Vout (Vdd) GSMopen high High High High High linear off off 0 to loop output opera- 3.6V tion middle Low High High High off linear on 0 to output opera- 1.5 Vtion low Low Low High High off linear on 0 to output opera- 1.0 V tionpower Low Low High Low off off off — cutoff CDMA or high High High LowHigh Com- off off Vb (3.6 V) GSM output plete closed on loop middle LowHigh Low High off com- on set output plete volt- on age of 1 to 2 V orless low Low Low Low High off com- on set output plete volt- on age of1.0 V or less power Low Low Low Low off off off — cutoff

Owing to the application of the present embodiment, the DC—DC converter232 is operated in the very low range of the required output level inthe system of the GSM open loop type to supply a power supply voltage toa high frequency power amplifier 210. It is therefore possible toenhance power efficiency.

The power supply circuit according to the embodiment shown in FIG. 10has a configuration similar to the power supply circuit shown in FIG. 3.A point of difference resides in that in the power supply circuit shownin FIG. 3, the DC—DC converter 232 and the power control circuit 233 arerespectively configured as the discrete semiconductor integratedcircuits, whereas in the present embodiment, the DC—DC converter 232 anda portion excluding the feedback circuit FDC of the power controlcircuit 233 are formed on one semiconductor chip so as to be configuredas a power semiconductor integrated circuit PSL.

In the present embodiment as well, there are provided two terminals foroutputting a signal for controlling gate terminals of external MOSFETs(MOSFET 231 in FIG. 3). A switch 236 for selectively connecting the twoterminals P1 and P2 to an output terminal of an op amplifier OPA isprovided on a chip. There is further provided a terminal P3 forconnecting a resistor Rfd and a capacitor Cfd constituting the feedbackcircuit FDC of the op amplifier OPA as external parts. The selectorswitch 236 is controlled by a signal outputted from a control logic CTL,based on control signals CONT0 through CONT2 supplied from a base band &modulation unit 300. Incidentally, although not apparent on the drawing,a power supply voltage Vb is applied to a terminal on the non-selectionside, which is disconnected from the switch 236, and hence anon-selected one of P-channel MOSFETs 231A and 231B is brought to an offstate.

Further, in the present embodiment, the power semiconductor integratedcircuit, the P-channel MOSFETs 231A and 231B (PMOS-A and PMOS-B) forpower supply, the resistor Rfd and capacitor Cfd, and output-feedbackbleeder resistors Rb1 through Rb3 of the DC—DC converter 232 arepackaged on one ceramic substrate so as to be configured as a powersupply module 230′.

As shown in Table 2, when a high output level in a GSM open loop isrequested, the PMOS selector switch 236 is switched to the P-channelMOSFET 231A (PMOS-A) so that the P-channel MOSFET 231A (PMOS-A) iscontrolled by the output of the op amplifier OPA, whereby a voltage Vdd,which changes linearly according to a signal Ramp inputted from the baseband & modulation unit 300 at this time, based on the power supplyvoltage Vb outputted from a battery 400, is supplied to itscorresponding high frequency power amplifier 210. At this time, theDC—DC converter 232 is brought to a non-operating state by a signaloutputted from the control logic CTL.

On the other hand, when a middle output level is requested or a lowoutput level is required, the PMOS selector switch 236 is changed overto the P-channel MOSFET 231B (PMOS-B) so that the P-channel MOSFET 231B(PMOS-B) is controlled by the output of the op amplifier OPA and theDC—DC converter 232 is brought to an operating state according to asignal outputted from the control logic CTL, whereby on the basis of astepped-down voltage generated by the DC—DC converter, a voltage Vdd,which changes linearly according to a signal Ramp inputted from the baseband & modulation unit 300 at this time, is supplied to the highfrequency amplifier circuit 210.

Further, the power supply module 230′ according to the presentembodiment is configured so as to be available even for the cases inwhich it constitutes such a CDMA system as shown in FIG. 4 and such aGSM closed-loop type system as shown in FIG. 6. Described specifically,when the P-channel MOSFET 231A or 231B (PMOS-A or PMOS-B) located on theside selected by the PMOS selector switch 236 is turned on, the outputof the op amplifier OPA is brought to full amplitude to thereby hold theMOSFET located on the selected side in an on state, thus making itpossible to supply the voltage with almost no reduction in level.

While the invention made above by the present inventors has beendescribed specifically based on the illustrated embodiments, the presentinvention is not limited to the embodiments. It is needless to say thatvarious changes can be made thereto without the scope not departing fromthe substance thereof. While the embodiments shown in FIGS. 4 through 6have been described as the system configurations of the cellular phonededicated for the CDMA system, the cellular phone dedicated for theGSM-system open loop type, and the cellular phone dedicated for theGSM-system closed-loop type, respectively, each of the embodiments maybe configured as a cellular phone wherein the coupler 260′ for detectingthe output level of such a GSM high frequency power amplifier 210 asshown in FIG. 6 and the automatic power control circuit 270′ forcomparing the output level detected by the coupler 260′ and the requiredoutput level to thereby generate the bias voltage Vabc for the highfrequency power amplifier 210 are added to the system shown in FIG. 1and which is thus capable of operation even in a closed-loop mode foractivating the automatic power control circuit 270′, an open-loop modefor operating a Vdd generator comprising the op amplifier OPA and theP-channel MOSFET 231, and any mode for CDMA. In such a case, the powersupply circuit 230 can be utilized.

While the above-described embodiment has described the case in which theDC—DC converter, the voltage control transistor and the power controlsemiconductor integrated circuit for controlling the voltage controltransistor are packaged on one insulating substrate like the ceramicsubstrate and configured as the power supply module, an inductor and acondenser connected to an output terminal of a power supply system areformed inside the insulating substrate, and they may be configured as apower supply module inclusive of these.

Further, while the above embodiment has described the power supplycircuit for the high frequency power amplifier, which is capable ofperforming communications of the two types of the GSM system and theCDMA system, the invention can be applied to a power supply circuit fora high frequency power amplifier of a cellular phone capable ofperforming communications for a dual-band type and a CDMA system capableof handling or processing signals lying in such a frequency band as in aDCS (Digital Cellular System) using a 1710 to 1785-MHz band, forexample, and for a triple-band type and a CDMA system capable ofhandling signals of a PCS (Personal Communication System) using a 1850to 1915-MHz band.

Incidentally, while the present embodiment has used the system ofobtaining the respective control signals designated at SHDN, CONT0,CONT1 and CONT2 from the base band, a method of configuring a system forreducing signal lines and receiving a serial signal, providing a powercontrol integrated circuit with a determination circuit, and performingequal switching is also practically considered.

Advantageous effects obtained by a typical one of the inventionsdisclosed in the present application will be described in brief asfollows:

According to the present invention, a reduction in power consumption canbe realized. As a result, a cellular phone using a power supply circuitof the present invention brings about the effect of making a callingtime long and increasing the life of a battery. The invention can beused in a cellular phone capable of communicating according to aplurality of systems like a GSM system and a CDMA system, and a powersupply circuit capable of reducing power consumption can be realized.Even where a power supply circuit capable of performing complex controlwith multi-functioning of a cellular phone is configured, a power supplycircuit, which is reduced in the number of parts thereby reducing itssize, can be configured.

What is claimed is:
 1. A power supply system for a high frequency poweramplifier, comprising: a voltage converter circuit whichswitching-controls a current flowing through an inductor to therebygenerate a desired voltage; a voltage control transistor which outputs avoltage corresponding to a control voltage in response to a voltageoutputted from a power supply; and a power control circuit whichcontrols the voltage control transistor, wherein one or moresemiconductor integrated circuits and one or more electronic parts arepackaged on one insulated substrate, wherein in a first mode, thevoltage converter circuit is brought to a non-operating state upon ahigh output to turn on the voltage control transistor so as to outputthe voltage sent from the power supply to a power output terminal, andthe voltage converter circuit is operated upon a low output to output avoltage converted by the voltage converter circuit to the power outputterminal, and wherein in a second mode, the voltage converter circuit isbrought to a non-operating state to control the voltage controltransistor based on a first signal for designating an output level,thereby outputting a voltage corresponding to the first signal to thepower output terminal.
 2. The power supply system according to claim 1,wherein the voltage control transistor is a P-channel type field effecttransistor.
 3. The power supply system according to claim 2, wherein thepower control circuit includes an operational amplifier circuit whichhas a first input terminal to which the first signal is inputted and asecond input terminal to which a second signal corresponding to anoutput voltage is fed back, and which outputs the voltage correspondingto the first signal.
 4. The power supply system according to claim 1,wherein a filter circuit using a ferrite bead as an inductor isconnected to an output terminal of the voltage converter circuit.
 5. Thepower supply system according to claim 1, wherein the voltage convertercircuit complementarily on-off controls a first switch element and asecond switch element connected in series between a source voltageterminal and a reference potential terminal to allow a current to flowthrough the inductor connected between a connecting node of the firstswitch element and the second switch element and an output terminal,thereby outputting a voltage obtained by stepping down the voltageapplied to the source voltage terminal, and wherein when the firstsignal indicates a predetermined level or less, the voltage convertercircuit controls the second switch element so as not to turn on thesecond switch element and thereby outputs a desired voltage under aswitching operation of the first switch element.
 6. The power supplysystem according to claim 1, wherein the inductor connected to theoutput terminal of the voltage converter circuit, and a smoothingcapacitive element connected to the other end of the inductor arepackaged on the insulating substrate.
 7. The power supply systemaccording to claim 1, wherein the first mode is a mode for performing atransmit operation according to a GSM-system closed-loop type, and thesecond mode is a mode for performing a transmit operation according to aGSM-system open loop type.
 8. The power supply system according to claim1, wherein the first mode is a transmit operation according to a CDMAsystem, and the second mode is a transmit operation according to aGSM-system open loop type.
 9. A power supply system for a high frequencypower amplifier, comprising: a voltage converter circuit whichswitching-controls a current flowing through an inductor to therebygenerate a desired voltage; first and second power control transistorswhich respectively have drain terminals connected to a common poweroutput terminal and which control a voltage outputted from a powersupply and outputs the same to the power output terminal; a powercontrol circuit which controls the power control transistors; and aswitching circuit which is provided between the power control circuitand a control terminal for the first and second power controltransistors and allows any one of the power control transistors to beconnected to the power control circuit, wherein one or moresemiconductor integrated circuits and one or more electronic parts arepackaged on one insulating substrate, wherein in a first mode, thevoltage converter circuit is brought to a non-operating state upon ahigh output to control the first voltage control transistor based on asignal for designating an output level, thereby controlling the voltageoutputted from the power supply and outputting the same to the poweroutput terminal, whereas upon a low output, the voltage convertercircuit is operated and the second voltage control transistor iscontrolled based on the signal for designating the output level tothereby control the voltage outputted from the voltage converter circuitand output the same to the power output terminal, and wherein in asecond mode, the voltage converter circuit is brought to a non-operatingstate upon a high output to output the voltage sent from the powersupply to the power output terminal via the first voltage controltransistor, whereas upon a low output, the voltage converter circuit isoperated to output the voltage converted by the voltage convertercircuit to the power output terminal via the second voltage controltransistor.
 10. The power supply system according to claim 9, whereinthe voltage converter circuit, the power control circuit for controllingthe first and second voltage control transistors, and the switchingcircuit are configured on one semiconductor substrate as a semiconductorintegrated circuit, and the semiconductor integrated circuit, the firstvoltage control transistor, and second voltage control transistor arepackaged on one insulating substrate so as to be configured as a module.